According to the current state of the art, stringing of a sports racquet, and installing the strings onto the racquet, is done manually with the help of a stringing machine. Known stringing machines are usually constructed with three main components: a racket mounting mechanism; a string tensioning mechanism; and a string clamping mechanism.
Typically, the racket mounting mechanism is used to hold the racket in a horizontal flat position during the stringing process and can be rotated horizontally in a full circle.
The string tensioning mechanism is a device used to tension the string, i.e., for pulling the string to the desired tension. The tensioning mechanism can function according to one of several known methods including drop weight, mechanic manual crank, electric, and electronic design. The components are usually fixed on the same common platform base of the stringing machine, so that the tension on the string can be created between them when the string is being tensioned.
The string clamping mechanism is used to hold string tension when switching strings. Commonly, it is one piece of string running back and forth multiple times on the racket either longitudinal or cross, or both.
As used herein, the singular term “string” refers to the string section between the two grommet holes, running longitude or cross on the racket head. The plural term “strings” as used herein refers to the all of strings inside racket between the two grommet holes, even though it is usually only one or two pieces of strings running through all the grommet holes for the whole racket.
Since the support frame of the string tensioning mechanism is normally at a fixed position relatively to the racket mounting mechanism, the stringing process is usually done on one string at a time. For each string, there are several steps to be completed repeatedly, namely: gripping the string on to the string tensioning mechanism; tensioning the string with the string tensioning mechanism; clamping the string by the clamp; de-gripping the string from the string tensioning mechanism; rotating the racket mounting system 180 degrees so the next string will be on the side of the string tensioning mechanism; threading the string through the grommet holes and weaving the cross string if the string is a cross string; and then repeating all of the steps above for this string. These steps are repeated for about 30 to 50 times, depending on type of racket, for stringing of a single racket. If it were possible to reduce even one step, or to simplify a step of the stringing method, it would save time and speed up the stringing process.
Among all the known tensioning methods mentioned above, each one has its own advantage and disadvantage. The drop weight method is simple in design, low cost, and hard to operate. It is commonly found on the low-end stringing machines. On the other end, the electronic tensioning mechanism can be operated by just one touch of a switch for tensioning, but is complicated in design, and very expensive. It is usually on a high-end stringing machine. The electronic tensioning mechanism can string a racket much faster than the drop weight type machine. The stringing machine with a mechanical manual crank is usually between the drop weight and electronic methods in efficiency. This is due to its design having a spring load inside which makes it need calibration periodically.
The mechanical manual crank also uses a locking mechanism to hold string after tensioning, and there is not a constant pulling (i.e., the string being tensioned is always under pulling force) compared to the electronic tensioning mechanism or drop weight tensioning mechanism (i.e., the string after being tensioned and, if held at fixed distance, the tension of string will drop a little bit with time.). The electric one (different from electronic tensioning method) uses the motor directly. It cannot achieve the uniform tension for every tensioning operation due to its design principle.
The drop weight stringing machine is usually constructed with a drop weight/bar, a horizontal axis for the drop weight to rotate up/down, a clutch or string grip/re-grip mechanism, and a support frame to hold these together. It utilizes the gravity force of the drop weight to pull the string. When the drop weight/bar reaches the horizontal position, the desired tension for the string is obtained. The support frame of the drop weight assembly is usually fixed to the common platform base of whole stringing machine, which is also the common platform of the racket mounting system.
Due to this design of a fixed support frame and its use of gravity to achieve the specific tension, after the gripping of the string, it is almost impossible to have the drop weight/bar reach the level position on the first try. When stringing, the clutch or string grip/re-grip mechanism must be adjusted to achieve the horizontal position of the drop weight/bar to obtain a desired tension on string. This adjustment of the string with the clutch or grip/re-grip mechanism usually needs several tries to get the drop weight/bar in the horizontal position. This is one of the most time-consuming parts of using the drop weight stringing machine.
If the adjustment is instead done by gripping/re-gripping the strings, it also may cause damage to the string. In fact, all these adjustments do is change the length of string on the pulley of the drop weight mechanism to achieve the desired tension on string, the drop weight bar in horizontal position, and certain string length between the racket and the pulley of the drop weight simultaneously.
Usually, the stringing process begins with the main/longitudinal strings, which is along the shaft direction of the racquet and will be called herein “main strings,” on the frame head. After the main strings have been installed and tensioned, the cross strings, which are perpendicular to the main strings, are installed by threading through a side grommet hole in racket, weaving through the main strings in the manner of a sinuous wave format, and threading through a grommet hole of other side out of racket. Here, the weaving of the cross string through the main strings means the cross strings go to a different side of the main strings, up in one main string and then down for next main string, etc. This process is normally performed by the fingers of the stringer—who push the cross string up and down (on the stringing machine) alternatively through the main strings, which requires significant skill and is time-consuming.
In this process, it is necessary to tension the main strings before weaving the cross strings, because it is almost impossible to weave the cross strings when the main strings are not tensioned in this manner, i.e., it will take even longer to thread the cross strings when the main strings are not tensioned. Pulling the cross strings through with tensioned main strings can cause heat to be generated by the friction between the main and cross strings. The heat generated can damage the main strings, i.e., the entire length of the cross string will rub the one spot of main strings. This effect is known as “heat burning.”
To avoid heat burning, when pulling the cross strings, the pulling must be slow and/or move the cross strings around main strings to a different position. For the badminton racket, after the main strings are tensioned, it is difficult to insert the cross string through the shared grommet hole due to the tensioned main string. Also, it is hard to move the tensioned main string in the grommet hole to generate space for the cross string to get through the same grommet hole. Commonly, an awl is used to help create some space in the grommet hole for the cross string to be inserted through the same grommet hole. However, this increases the probability of damaging the main string, which is already tensioned.
Various devices and products have been proposed to facilitate the placing/weaving of the cross strings and provide a clear spacing for the cross strings to pass through easily by displacing main strings in opposite directions, perpendicularly to the plane of the racquet head, and alternate main strings. Non-limiting examples are certain devices from Stringway Inc., a Dutch manufacturer of stringing machines, and devices described in U.S. Pat. Nos. 4,339,131, 4,270,752, and 3,994,496, and the device described in International Publication No. WO2013127375.
These known devices and associated methods will displace the main strings in the direction perpendicular to the main strings and racket plane surface for each crossing string as shown in FIG. 2. These devices put extra stress on the main strings due to the displacement perpendicular to the main strings. The extra stress may damage the main strings or reduce their lifespan. Also, some of these devices need proper alignment on the main strings before starting, which takes additional effort to do it.
Due to these draw backs, these designs have not found wide acceptance. Consequently, the conventional cross strings weaving technique that uses the fingers of a stringer is still commonly used during the racquet stringing. This requires significant skill and is time-consuming.
There is a continuing need for an apparatus and method for stringing a racket that is more efficient and less time-consuming relative to the prior art.